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Archaea
(ahr-keĀ“ә)
in the three-domain system of classification, one of the two large divisions into which prokaryotes are grouped. They are genetically distinct from bacteria and share some features with the eukaryotes. They have a variety of shapes and sizes, may or may not have a cell wall, and occur as single cells and as filaments or
aggregations. They live mainly in extreme environments, such as hot-water vents on the ocean floor. Some occur as symbionts
in the digestive tracts of animals. None cause disease in humans. Cf. Bacteria.

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